Casting process



. 1949- w. 8. RICE 2,480,048

CASTING PROCESS Filed July 10, 1944 ZULZZL'a/W 5121 68, BY

atented ug. 23, 1949 [TED STATES casrmo PROCESS William S. Rice,Chicago, 111. Application July 10, 1944, Serial No. 544,265

4 Claims. 1

This invention relates to casting, and has to do with a casting processemploying a low fusing mold which may readily be removed from thearticle cast therein so as to avoid injury to the cast article, such asmight occur if the mold were removed from the article by chopping orbreaking the mold as is done in casting articles in refractory molds.

My invention is directed to a casting process in which I provide a lowfusing mold, this mold having therein a casting cavity conforming to thedesired article to be cast, the mold, after casting of the articletherein, being removed, convenient- 1y by melting, so as to separate thematerial of the mold from the cast article without injury to the latter.In the more specific and preferred form of my process, disclosed hereinby way of example, I provide a mold formed of a metal fusible at atemperature which will not cause injury to or impairment of the articlecast therein, and fill the cavity of the mold with a suitable material,conveniently a material of a character to be heat cured and to set at atemperaure lower than the fusing temperature of the metal of the mold,the mold with the material therein being then heated to a propertemperature to cause curing and setting of the material, after which themold is heated to a higher temperature effective to cause fusing thereofwithout injury to the cast article, thereby melting the mold away fromthe article cast therein. Further objects and advantages of my inventionwill appear from the detail description.

In the drawings:

Figure l is a side View of a human ear illustrating the first step ofthe process of my invention, which consists in taking an impression ofthe ear cavity;

Figure 2 is a sectional View through a retaining ring disposed about theimpression produced by the step of Figure i, this impression serving asa pattern about which the low fusing material which constitutes the moldis poured;

Figure 3 is a sectional view through the mold produced by the operationof Figure 2, with the mold cavity filled with a casting material of acharacter to be heat cured and to set when cured, the mold with thecavity thereof filled with the casting material bein subjected to heattreatment at a temperature below the fusing or dissolving temperature ofthe mold, there being a cover on the mold to protect the castingmaterial from the heating medium;

Figure 4 is a view similar to Figure 3 but illustrating the step ofremoving the mold by fusing thereof away from the cast article;

Figure 5 is a side view of the cast article remaining after fusing ofthe mold;

Figure 6 is a sectional view, with the article to be reproduced shown inelevation, illustrating the first step of the process of my invention asapplied to producing a cast of a tooth, this first step consisting inmakin an impression of the tooth;

Figure 7 is a sectional view, partly in elevation, illustrating thesecond step consisting in making a casting from the mold produced by theoperation of Figure 6;

Figure 8 is a sectional view, partly in elevation, of a ring disposedabout the casting produced by the operation of Figure 7, illustratingthe step of pouring the low fusing material from which the mold is to beformed about the casting as a pattern;

Figure 9 is a sectional view of the mold produced by the operation ofFigure 8, with the mold cavity filled with a casting material of acharactor to be cured and to set when subjected to heat treatment at atemperature lower than the meltin temperature of the mold, illustratingthe step of heat treating the material in the mold cavity;

Figure 10 is a view similar to Figure 9 but illustrating the step ofmelting the mold from about the article cast therein; and

Figure 11 is a side view of the article cast in the mold after the moldhas been melted from the cast article.

In applying devices to aid deaf people in hearing, commonly termedhearing aids, it is important that the instrument which goes into theear fit the ear cavity accurately and comfortably so as to be retainedin proper position therein and not cause undue discomfort to the user.Under present practice considerable delay in fitting such devices isincurred due to the necessity of having the patient present for thefitting, which also frequently causes considerable loss of time by thepatient. By making an accurate reproduction of the patients ear cavityand shaping the instrument which goes into the ear accurately inaccordance with this reproduction, an accurate and comfortable fit ofthe instrument can be assured and the delay incident to waiting untilthe patient is available for fitting the instrument to his car, as wellas the loss of the patients time, can be avoided. In Figures 1 to 5,inclusive, I have illustrated the process of my invention as applied tocasting an article, in the nature of a plug, corresponding accurately tothe cavity of a persons ear, this article serving as a guide inconstructing an instrument to be fitted into the car, by means of whichthe instrument can be so formed as to provide for an accurate andcomfortable fit.

In Figure 1 an impression of thepavity or a persons ear e is taken byinserting nto the ear a suitable known impression material l2, thisoperation being performed in a known manner, and any suitable impressionmater al which when set will retain the shape into whlch it has beenformed may be used. For example, an impression plaster composition maybe used, though I preferably use the impression material known conmercially as Coeloid made by Coe Laborator es, Inc., of Chicago,Illinois. The latter impression material-Coeloi -after it has setsufficiently to retain the shape to which it has been formed possessesappreciable elasticity, which is desirable in certain cases as will beexplained later. a

The impression taken as in F gure 1 produces a plug shaped articlei3,shown in Figure 2, con forming to the ear cavity from which the1mpression is taken. After this article i3 has taken its completese t itis placed flatwise upon a supporting s face, as. in Figure 2, and a reain: ing ring i l, formed of a metal or alloy having a high fusingtemperature, is placed upon the supporting surface about the article i3,which serves as a pattern. The ring it is then filled to a suitabledepth with a material i5 which may readily be removed, conveniently byapplication of heat at a suitable temperature to cause melting or fusingof the material [5, this ma erial serving as an investment for thearticle or pa ttern i3 and being of a character to set about the sameand Within the ring I4. Conveniently the material I5 is an alloyconsisting of 41.67% tin, 16.67% lead and ll.66% bismuth, having afusion point of 212 F. Alternatively, an alloy consisting of 50% lead,30% tin and b1smuth, hav ing a fusion point of 202 F. may be used. Themolten alloy is poured from a suitable crucible or ladle l6 into thering M, as illustrated, it being understood that the material of whichthe plug or pattern It. is formed is of such character as not to beimpaired 'or in any way m uriousl y affected by the 'molt'en alloy withwhich it is invested. After. the investment material or alloy 15 hasset, the pattern I 3 is removed therefrom, b breaking the pattern andremoving the parts thereof where necessary, if this pattern be formed ofplaster or other non-elastic material, or if the pattern be'formed of amaterial which when finally set possesses appreciable elasticity, I ofwhich there are known materials including. Coeloid above -referred to,the pattern may be removed as a unit. That provides a mold comprising aheat destructible body formed of the mateial or alloy, l5, within thering [4, having therein casting cavity'conforming accurately to t epattern [3. The alloy used should be such as -t to have objectionabledimensional change in cooling from its melting point to roomtemperature, as will be understood by those familiar with the castingart, and the retaining ring is preferably should be of a metal or alloyhaving a fusion point or temperature considerably above that of theinvestment alloy.

After the mold has been produced in the above manner, the cavity thereofis filled, with a suitable material for' producing the desired castarticle. This casting material should be'a settable material of suchcharacter as to fill completely and accurately all portions of; thecasting cavity in the mold and not to be impaired or injured attemperatures required to destroy or dissolve the mold away from the castarticle. Preferably, I employ a casting material which may be cured andwill set at a temperature appreciably lower than the fusing temperatureof the mold and which, when cured and set, has a fusing temperaturesufiiciently higher than that of the mold so that it will not besoftened to an objectionable extent or otherwise impaired or injured inthe melting of the mold. I have found that an acrylic resin is wellsuited for the casting material. The resin which I preferably use ismethyl methacrylate, which I mix in powder form with a suitable liquid,such as acrylic acid in its mono mer form, to provide a plastic mix ofsuitable consistency for packing into the mold cavity so as to enterinto and completely fill all of the portions thereof. In Figure 3 themold is shown with the cavity thereof filled with castire material !8,such as that above referred to, or any other suitable materiaL'afterwhich th top of the mold is covered so as to be effectively closed by aslab or plate IQ of considerable thickness seating upon the upper end ofthe mold so as to close the latter, particularly the upper end of themold cavity, and retain the casting material. [8 therein. The mold, withthe contained casting material and closed by the slab id, is then immersed in a bod of a suitable liquid 25, con veniently Water, within acontainer 25, the mold seating at its lower end upon a grate 22 ofsuitable height resting upon the bottom wall of the container. Theliquid 20. within the container 2'! is then heated in any suitablemanner, as by means of a burner 23', to a temperature below the fusingtemperature of the mold but sufiiciently high to heat the mold and thecasting material therein to the curing temperature of the latter, whichis from 169 F. to F; when using the methyl methacrylate compositionabove mentioned. During this curing operation, the cover 19 seals theupper end of the mold against access of water to the casting materialand also prevents escape of the latter from the mold cavity. Thematerial 58 tends to expand somewhat during the curing operation sinceit is restrained against escape from the mold cavity by the cover l9, itis cast under pressure which is desirable as assuring accuratereproduction of the fine details of the mold cavity.

After the material l8 has been cured and has set, it will not beinjuriously affected by the liquid or water 20, it being understood thatthe liquid used as a heating medium is of a character not to injure thematerial I8 after curing and setting thereof. The cover I9 may then beremoved or not, as desired, and the temperature of the water 20 is thenincreased sufficiently to cause melting of the mold so as to free thecast article 24, as shown in Figure 4 in which the major portion of themold has been melted. The material of the mold, as it is melted, passesdownwardly through the grate 22 into the lower portion of the container21, and when the mold has been completely melted the article 24 restsupon the grate and is completely freed of the material of the mold. Itwill be seen that the curing operation. and the operation of melting themold may be. performed as, in effect, a continuous operation, which isconducive to expedition and facility in casting the. article and freeingit from the mold. By melting the mold fromv about the cast article, riskof injury to the latter is avoided and the article as cast conformsaccurately to the pattern about. which the mold was 5 formed. The-castarticle-may-then be treated with acid solution, or in any other suitablemanner, for removing any dross that may remain thereon, thefinished'article 24 then appearing as in Figure 5. This articl is anaccurate reproduction of the original impression or plug and may safelybe relied uponin making aninstrument to fit into the car from which theoriginal impression was taken, with assurance that an instrumentconforming to'the castarticle 24 will fit accurately and comfortablyinto the ear from which the impression was taken and will be properlyretained therein.

Since the impression taken in Figure 1 is a positive impression, that isan impression of the inside of the ear, that impression may be useddirectly as the pattern for forming the corresponding cavity in themold. Where a negative impression is originally taken, for example theimpression of a tooth, it is necessary to make a positive of theimpression, which positive is then used as a pattern for forming thecavity in the mold. The process in the latter case is essentially thesame as that above described, with the exception of the preliminarysteps for obtaining the pattern for use in producing the mold.

Referring to Figures 6 to 11, inclusive, in Figure 6 I have illustratedthe steps of taking an impression of a tooth, such as a molar 25 in amold 26, preferably formed of Coeloid, though this mold may be formed ofany other suitable known impression material which when set possessessufiicientelasticity to permit of removal of the tooth 25 from the moldwithout adversely affecting the accuracy of the impression therein. Themold 25 is of cylindrical form and, after this mold has set, it isplaced within a suitable retaining ring 27 fitting closely about themold and extending a suitable distance there above, the underface of themold and the lower end of the ring resting upon a suitable fiatsupporting surface. The cavity of the mold 2B, and the ring 21 to asuitable height above the mold, are then filled with a suitableimpression material in liquid form, which when set is elastic butsufficiently rigid to retain its form into which it is shaped by themold cavity, this material being poured into the mold cavity and thering from a suitable container 28, as shown in Figure 7. In thatconnection, no difiiculty arises from using the same material for themold 26 and for producing therefrom the desired pattern, since thisimpression material Coeloid -when set, will not adhere to the samematerial poured in contact therewith. Any other suitable impressionmaterial may be used, if desired, for forming the desired pattern ormodel from the mold 26. After the impression material which has beenpoured into the cavity of the mold 26 and into the ring 21 has set, theresultant model, comprising a disc-shaped plate 30 and a pattern 3|integral with and projecting from the plate 30, conforming to the cavityin mold 26, is removed from this mold, that being permitted by theelasticity of mold 2t and, preferably, of the-mold material of which thepattern is formed.

After the pattern has been produced in the manner above explained, it isplaced upon a suitable flat supporting surface with the pattern 3|disposed upward, and a retaining ring is then placed about the baseplate 30, fitting snugly thereabout with its lower end in contact withthe supporting surface, the pattern 3| being disposed centrally withinthe ring as shown in Figure 8. The pattern is then invested with a lowIt will be understood,

fusing material, such as'the alloy above referred to, poured into thering from the ladle or crucible l6, as before. After the investmentmaterial I 5 has set, the pattern 3| is removed therefrom providing alow fusing mold having therein a casting cavity conforming accurately tothe pattern 3|. This cavity is then filled with a casting material, suchas the methyl methacrylate composition above described. The top of themold is then closed'by a cover IQ of considerable weight, as and for thereasons above set forth. The mold, with the contained'casting material,is then heated to proper temperature for effecting curing and setting ofthe casting material, and the mold is then melted away from the castarticle. In Figure 9 the casting material is indicated by the referencenumber IB since the shape of the mold cavity is different than in Figure3, though it will be understood that the casting material is the same,or may be the same, in both cases.

Instead of heating the mold and the contained casting material inliquid, the mold may be passed upon a traveling grate 33 moving atappropriate speed through a furnace 34 of any suitable knownconstruction. This furnace 34 has graduated. heating zones, as is known,such that during the first portion of the travel of the mold through thefurnace the mold is heated to a proper temperature for effecting curingand setting of the casting material E8 while avoiding heating of themold to a sufficiently high temperature to cause objectionable softeningor fusing thereof. After completion of the curing and setting of thematerial la the mold passes into the higher temperature zone of thefurnace, Where it is heated to a sufiiciently high temperature to cause;melting of the mold, thereby melting it away from the cast article, themelted material of the mold passing downward through the grate 33 into asuitable trough or tray 35 so disposed that the mold passes thereaboveduring the operation of melting the material of the mold. The castarticle thus freed from the material of the mold rests upon the grate 33from which it may be removed, the melting operation for removing thebody of the mold being shown in Figure 10, in which the major portion ofthe mold has been melted away. The cast article from which the mold hasbeen removed may then be treated with acid, manner, to remove therefromany remaining dross, and then appears as in Figure 11, the article 36accurately reproducing the pattern 35 and, therefore, accuratelyreproducing the original tooth 25.

Heating of the mold in water, particularly for melting the mold, isadvantageous as preventing objectionable oxidation of the alloy whichmay be recovered and reused for succeeding molds. however, that the moldmay be heated in any suitable manner and, where desired or necessary,such heating may be effected within a suitable atmosphere to preventoxidation or other action on the mold material such as would interferewith its being reused.

In the production of impressions or plugs, as above described, thesearticles are unique or individual to the persons from which theimpression has been taken and, since ordinarily but one cast article isrequired, there is no particular reason for retaining the mold which maybe destroyed for the purpose of removing the cast article therefrom, asabove explained. Likewise, in the casting of teeth and other articleswhich or in any other suitable are to be retained as reference samples,there is no particular reason for retaining the mold. It will beunderstood, however, that the casting process of my invention may beused to advantage in cases where it is desired to reproduce an articlein considerable numbers, and provides an inexpensive and high speedcasting method for that purpose.

In general, the method of my invention comprises forming a mold of a lowfusing material, such as an alloy or other material which may bedestroyed by the application of heat or in any other suitable manner,and casting in this mold, from a suitable material, the desired article,the mold being then melted so as to free the cast article without riskof injury thereto, such as might occur if the mold were removed from thecast article by breaking up or cutting away the material of the mold.

I claim:

1. The steps in the method of making an article of the class described,which comprise forming a mold body of relatively low fusing metal abouta pattern and subsequently removing said pattern to leave a mold cavity,filling said cavity with a material curable at a temperature below therelatively low fusing temperature of the mold body, heating the moldbody and the material in said cavity to a temperature sufficiently highto cure said material and to form a cured article but below the fusingtemperature of the mold body, and thereafter as a continuous processwith said curing operation increasing the heat to heat the mold body toits fusing temperature to melt the same but below the temperature whichwill deleteriously affect the cured article.

2. The steps in the method of making an article of the class described,which comprise forming a mold body of relatively low fusing metal abouta pattern and subsequently removing said pattern to leave a mold cavity,filling said cavity with a material curable at a temperature below therelativel low fusing temperature of the mold body, heating the mold bodyand the material in said cavity to a temperature sufficiently high tocure said material and to form a cured article but below the fusingtemperature of the mold body, thereafter as a continuous process withsaid curing operation increasing the heat to heat the mold body to itsfusing temperature to melt the same but below the temperature which willdeleteriously affect the cured article, and permitting the molten moldmaterial to flow away from the cured article during the application ofthe heat for melting the mold body,

3. The steps in the method of making an article of the class described,which comprise forming a mold body of relatively low fusing metal abouta pattern and subsequently removing said pattern to leave a mold cavityopening from one side of the mold body, filling said cavity with aresinous material curable at a temperature below the relatively lowfusing temperature of the mold body and which tends to expand whenheated to cure the same, applying closure means over the open side ofsaid cavity, heating the mold body and the material in said cavity to atemperature sufficiently high to cure said material to form a curedarticle and to cause said resinous material to tend to expand but belowthe fusing temperature of the mold body, utilizing said closure means torestrain said resinous material against escape from the mold cavityduring the curing operation whereby to mold said resinous material underpressure, thereafter as a continuous process with said curing operationincreasing the heat to heat the mold body to its fusing temperature tomelt the same but below the temperature which will deleteriously affectthe cured article, and permitting the molten mold material to flow awayfrom the cured article during the application of the heat for meltingthe mold body.

4. The method of making an article of the class described, whichcomprises forming a pattern of the article, placing the pattern on asupporting surface, placing a retaining ring upon the supporting surfaceabout said pattern, introducing to suitable depth in said ring and aboutsaid pattern a molten'metal fusible at a relatively low temperature toform a mold body and allowing same to set, removing the pattern fromsaid mold body to form a mold cavity therein, filling said cavity with amaterial curable at a temperature below the relatively low fusingtemperature of the mold body and adapted to constitute the body of thefinished article, placing the ring having therein the mold body withsaid last mentioned material in the mold cavity thereof in invertedposition upon a grate, heating the material in said cavity to atemperature sufficiently high to cure said material to form a curedarticle but below the fusing temperature of the mold body, thereafter asa continuous process with said curing operation increasing the heat toheat the mold body to its fusing temperature to melt the same but belowthe temperature which will deleteriously affect the cured article, andpermitting the molten mold material to flow away from the cured articleduring the application of the heat for melting the mold body.

, WILLIAM S. RICE.

REFERENCES CITED The following references are of record in the file ofthis patent:

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